<!DOCTYPE html>
<html>
<head>
	<meta charset="utf-8">
	<title></title>
	<style type="text/css">
		div{
			width: 50px;
			height: 50px;
			background-color: red;
		}
		span{
			background-color: blue;
		}
	</style>
</head>
<body>
	<div>
		<span>123</span>
	</div>

	<script type="text/javascript">
		var div = document.getElementsByTagName('div')[0];
		var text = document.createTextNode('比好');
		div.appendChild(text);
	</script>
</body>
</html>